1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to radio frequency identification (RFID) communication systems including RFID readers that communicate with RFID tags.
2. Background Art
Radio frequency identification (RFID) tags are electronic devices that may be affixed to items whose presence is to be detected and/or monitored. The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored wirelessly by devices known as “readers.” Readers typically have one or more antennas transmitting radio frequency signals to which tags respond. Since the reader “interrogates” RFID tags, and receives signals back from the tags in response to the interrogation, the reader is sometimes termed as “reader interrogator” or simply “interrogator”.
With the maturation of RFID technology, efficient communications between tags and interrogators has become a key enabler in supply chain management, especially in manufacturing, shipping, and retail industries, as well as in building security installations, healthcare facilities, libraries, airports, warehouses etc.
In a RFID system, typically an interrogator transmits a continuous wave (CW) or modulated radio frequency (RF) signal to a tag. The tag receives the signal, and responds by modulating the signal, “backscattering” an information signal to the interrogator. The interrogator receives signals back from the tag, and the signals are demodulated, decoded and further processed.
A recent RFID standard specifies communication parameters for a 2nd generation of RFID systems, known as “Gen 2 RFID systems” with extended data transmission capabilities, including different modulation and encoding techniques, and a wide spectrum of bit rates. The high speed transmission of data according to Gen 2 requires more sophisticated signal processing procedures which provide high performance in terms of bit error rate (BER) and block error rate (BLER), in as simple an implementation of both tags and readers as possible.
Advanced RFID systems need considerable increase in their data rates. The Gen 2 RFID specification is designed to provide a high bit rate. However, Gen 2 RFID systems have limited ability for data rate improvement because they utilize binary signals. This “two-position” limitation is caused by specific problems of tag implementation. Improvements in data rate are possible based on the utilization of multi-position signals. Some advanced research and development is in progress in this area. Multi-amplitude-phase mapping techniques, such as QAM (Quadrature Amplitude Modulation), are being researched for future RFID systems. Such RFID systems, if successful, could provide a higher bit rates than existing binary RFID systems at the same frequency bandwidth. However, limitations on tag and interrogator complexity prevent utilization of QAM signal processing in present RFID systems.
Thus, what is needed are ways of integrating multi-position signal technology into RFID systems to provide higher bit rates.